1. Field of the Invention
This invention relates to a quick-release type clamping assembly for releasably or removably mounting a wheel hub to a pair of fork ends of a bicycle frame, and more particularly to such clamping assembly which is improved to prevent unexpected removal or detachment, from the fork ends, of the hub in its mounted condition.
2. Description of the Prior Art
In bicycles, generally, it is often required to remove a wheel hub from a pair of fork ends of a bicycle frame for replacement or repair, for example. For this purpose, Japanese Utility Model Application Laid-open No. 57-171902 discloses a quick-release type clamping assembly for a bicycle hub which enables quick removal of the hub when required.
More particularly, the clamping assembly of the above laid-open utility model application comprises a tie rod extending through a tubular hub shaft on which a hub shell is rotatably supported between a pair of fork ends. The tie rod has one end screwed to a nut positioned axially outwardly of one fork end. The other end of the rod is provided with an enlarged head positioned axially outwardly of the other fork end and having a cam hole extending transversely of the rod. A hollow presser member is fitted around the enlarged head and axially movable relative thereto toward and away from the nut. A lever, which is pivotable about a pivotal axis between a clamping position and a releasing position, is mounted to the presser member and has a cam portion received within the cam hole and eccentric relative to the pivotal axis.
When the lever is pivoted to the clamping position, the presser member is moved axially inwardly toward the nut due to the eccentricity of the cam portion. As a result, the distance between the nut and the presser member is reduced to clamp the hub (hub shaft and hub shell) to the fork ends.
Conversely, when the lever is pivoted to the releasing position, the presser member is moved axially outwardly away from the nut, so that the hub and the fork ends are relieved from the previous clamping force to enable ready removal of the hub (wheel).
As described above, the quick-release type clamping assembly has an advantage of enabling quick mounting and removing of the hub. However, such a clamping assembly has a disadvantage that the hub (wheel) can be unexpectedly removed during cycling when, for example, the lever accidentally comes into contact with a foreign object and is thereby pivoted in the releasing direction. In other words, the advantage of the quick-release type clamping assembly also leads to a serious disadvantage.
In order to overcome such a disadvantage, the quick-release type clamping assembly of the above described Japanese laid-open utility model application further comprises a lock member having a threaded shank for adjustable screw engagement with an axial threaded hole formed in an axially outer end wall of the presser member. The threaded shank of the lock member has a front end which, when screwably advanced, comes into abutment with the cam portion of the lever to frictionally prevent unintended pivotal movement of the lever from its clamping position.
The lock member of the prior art, however, is still insufficient in completely preventing unexpected pivotal movement of the lever and resultant removal of the hub. This is because the threaded shank of the lock member comes into contact with the cam portion of the lever at a relatively small distance from the pivotal axis of the lever, whereas the lever has an arm portion extending a substantial length from the pivotal axis. Thus, even a relatively small force on the arm portion of the lever can overcome the friction between the cam portion and the lock member shank portion to cause unexpected pivoting of the lever from the clamping position.